When former ad buyer
Samantha Giangrande
began looking to return to work recently after a two-year child-rearing break, she noticed an unsettling fact: the advertising world she knew had changed.

"I'm 37 years old and extinct," she said, lamenting that all the agencies she talked to about a job were obsessed with something she didn't possess—digital experience.

Once home to creative types in the mold of Don Draper and "Mad Men," Madison Avenue is increasingly a bastion of geeks: computer programmers, data heads and quantitative analysts.

People "with traditional backgrounds aren't getting hired," said
Amy Hoover,
president of Talent Zoo, an Atlanta-based company that operates an online job site specializing in the ad business.

That shift is causing a bit of existential anxiety. "If there's one word that applies to this industry, it's fear," said
Bill Crandall,
a consultant to Della Femina Advertising, where he worked as the chief marketing officer before his position was eliminated in 2011. "I never fathomed this going into the industry."

Don Draper of 'Mad Men' never had to worry about digital upheaval.
AMC/Associated Press

He has been trying to land a full-time advertising job and has watched colleagues in the industry struggle to make a comeback. "It's like trying to get a seat on a plane that is booked solid," he said. "The people who are out of work are on standby."

Last month's merger agreement between New York-based
Omnicom Group Inc.
and Paris-based Publicis Groupe SA only intensified the nervousness. The two ad giants, whose combined stock-market value totaled $35.1 billion, touted their marriage as driven in part by the rise of big data and digital advertising. Some employees are fretting about possible job cuts, though the two companies have said their deal wasn't about that.

"This wasn't done just so we could go in and cut jobs," said
John Wren,
Omnicom's chief executive, in an interview last week

Even so, with all the talk about the importance of data to Omnicom and Publicis, the "creative people can't help but feel left out," said
Mike Sheehan,
chairman of Hill Holliday, a Boston-based ad agency owned by
Interpublic Group
of Cos.

Mr. Sheehan, whose parent company is itself now the subject of takeover speculation, dislikes the new emphasis.

"Algorithms cannot give people goose bumps, and algorithms cannot tell a story," said Mr. Sheehan. They "cannot give you that nugget of insight that differentiates brands and products," he added, "That is only performed by human beings that can tell stories and can understand consumer behavior instinctively."

The trend toward digital advertising has been under way for about a decade. This year digital ad spending in the U.S. is expected to grow nearly 14% to $41.9 billion, or about 25% of total ad spending, according to eMarketer.

Traditional ad agencies eventually embraced digital media, initially the province of specialist firms, often by acquiring those firms, hiring digital-savvy executives or training staffers in new techniques. As the new executives moved in, some people thought to be too invested in the old ways were dismissed.

Times got tougher during the recession. U.S. ad spending fell just over 12% in 2009. Omnicom cut its workforce to 63,000 by the end of 2009 from 70,000 in 2007, according to the company's annual report. Interpublic cut 5,000 jobs between 2008 and 2009, ending that year with 40,000 employees, company filings show.

While both companies have added back staffers since then—Omnicom is now bigger than it was in 2007—the growth has largely focused on digital advertising, executives have said.

For several years, Publicis USA, an ad agency owned by Publicis, has had a policy of requiring new hires to have some digital experience, according to people familiar with the matter.

Early on, the creative side of the business was affected, as executives had to learn how to write search ads, create interactive ads, and craft campaigns that would resonate on social-media sites. At the same time, media buyers, the executives who buy ad time and space on behalf of marketers, had to figure out where to find consumers, who were spending more time online.

More recently the media-buying part of the business has undergone another wave of change, thanks to the digital revolution. More digital ads are bought through automated exchanges, a process known as "programmatic buying."

It is a far cry from the days when media schedules were faxed back and forth and relationships between ad-sales executives and media owners were cemented by long nights of schmoozing over drinks.

So far, automated real-time bidding accounts for a relatively small part of total media spending. But it is on the rise. According to eMarketer, U.S. advertisers will spend $3.4 billion on real-time bidding for online display ads in 2013, up 73% from last year.

Although the rise of automated trading has meant adding new types of executives it also will likely have a downside: job cuts for conventional media buyers.

"If you are on the analytics and digital side of things that is where the bulk of the jobs are," said Talent Zoo's Ms. Hoover. Five years ago traditional media buying and planning job placements accounted for about 25% of Talent Zoo's business. Now it is about 5%, she said.

While some ad executives are nervous, for others the massive changes haven't "sunk in yet," said
Joe Grimaldi,
chief executive officer of Mullen, an ad agency owned by Interpublic. "Looking ahead a few years, a lot of those roles will not exist," he added. Someday, he said, automation some of the business of buying TV ads will be automated.

"Everyone worries about their jobs," said
Paul S. Gumbinner,
founder and president of Gumbinner Co., a recruiter whose clients include Publicis Kaplan Thaler and Omnicom's BBDO. "There's no loyalty."

Mr. Gumbinner said that the industry's consolidation has unsettled its ranks. "If you're a Don Draper-level person, you're probably protected by contracts. But for 90% of employees, the smart ones understand they need a Plan B. It's a really tough business."

Even those with jobs in digital advertising are uneasy. "Everyone is overworked and stressed," said
Jon Bond,
co-founder of an ad firm now called Kirshenbaum Bond Senecal + Partners, who currently runs a digital firm Tomorro LLC, a holding company of digital marketing and media assets.

In the past, Mr. Bond said, an agency on average might have produced three print ads and three commercials a year for a typical client. The Web, with its constant stream of new content, has changed the demand. "Now you have to do the equivalent of that every week," he said.

"Look at 'Mad Men' when they could go out drinking and come back three hours later and come up with an idea," Mr. Bond said. "Now they go to Starbucks and get caffeine. The double latte is the new double martini."

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